Differential gear assemblies are utilized in vehicles to translate drive (pinion) shaft rotation into left and right axle shaft rotation, which in turn provides drive force at the wheels. Conventional vehicle differential assemblies allow the wheels to rotate at different rates. This is necessary during vehicle turning when the outside wheel will rotate faster than the inside wheel. This is commonly accomplished through the use of differential side gears and pinion gears located inside the differential case. The differential side gears, each splined to an axle shaft, rotate relative to the differential case and relative to each other. This process is called differentiation, and allows the vehicle to be turned without causing the tires to slip along the road.
One form of differential assembly is commonly known as “open” differential. An “open” differential is a differential assembly without a torque biasing mechanism. In such a system, when the vehicle is driving straight, and a difference in road friction, or traction, exists between the right and left tires, the rotational motion of the differential is transmitted mostly to the wheel with the least grip/lower friction. It is further known that in such “open” differentials, the maximum torque delivered to both wheels is twice the torque delivered to the wheel with less traction. This means that if one tire is placed on a low friction surface, it receives almost zero driveline torque. In addition, the other tire also receives almost zero torque, regardless of the traction available at that tire. To further exacerbate these characteristics, if the torque delivered to the wheel with the less traction exceeds the friction torque acting on the tire-road interface, the wheel may slip. Since the coefficient of dynamic/sliding friction is commonly less than the static/non-sliding friction, a slipping wheel has even less traction than when it is not slipping. Thus, the torque delivered to both wheels is further reduced.
It is known that if the relative motion between the two side gears can be stopped or limited, then both wheels will be forced to rotate at the same speed as the differential, regardless of any difference in traction between the differentiated wheels. By reducing the relative motion, differentiation can be essentially stopped. Unequal amounts of torque can be sent to each wheel, proportional to the difference in traction between the two wheels. This allows the torque to be delivered where it can best be utilized. The mechanism which applies more torque to the wheel with higher traction, yet still allows differentiation, is called a limited slip differential (LSD), a torque-biasing differential, positraction, etc. There are several different types of LSDs including clutch-type LSDs, viscous couplings, “locked” differentials, and Torsion® differentials. Known torque biasing differentials often rely on a friction interface between one of the differential gears (side gear, pinion gear, or reasonable facsimile) in the differential case (the differential gear container which is attached to the ring/driven gear and receives torque from the pinion/driving gear).
Yet another mode known for the operation of a differential includes a so-called “disconnected” mode. In this mode, the “disconnected” wheels are free to rotate independently from each other. This mode is desirable, for example, in a two wheel drive vehicle when two wheels of a non-driving axle are allowed to spin independently from the two wheels of a driving axle. As such, the non-driving axle wheels are “disconnected” from each other and from the driving axle wheels. This mode may be desirable, for example, to improve fuel economy during highway driving situations (i.e., by reducing overall friction forces associated with operating the differential).